This invention relates to a process for preparing diphenylalkanes.
Brominated diphenylalkanes, e.g. decabromodiphenylethane, are recognized flame retardants for use in various thermoplastic formulations. These flame retardants can be formed by partially or totally brominating diphenylalkane with a brominating agent, e.g. Br.sub.2 or BrCl, in the presence of a Lewis acid catalyst.
Despite the efficacy of brominated diphenylalkanes as flame retardants, their acceptance as a commercially viable product has been hampered by their cost. The largest factor contributing to their cost is the cost of the starting material, diphenylalkane. Most processes for producing diphenylalkane are characterized by their low yields and/or by their complexity. For example, diphenylethane can be produced by reacting benzyl chloride in an aqueous medium with iron powder (99.9.sup.+ % pure iron). While this reaction is relatively simple, the yield is only about 16%. Higher yields can be obtained by other processes, but such yields come with a loss in process simplicity and the use of more expensive reagents. Exemplary of such processes, is the process described by Wada et al in "The Reductive Coupling Reactions of Benzyl Chloride by Copper (I) Complexes" , Bulletin of the Chemical Society of Japan, Vol. 41, Pages 3001-3007 (1968). This process effects the coupling of benzyl chloride by reacting same with a Cu(I) complex. The Cu(I) complex is obtained by providing a complexing agent, e.g. ethylenediamine, diethylenetriamine, triethylenetetramine, acetylacetone, or EDTA to the reactin mixture which contains cuprous chloride, a reaction solvent and benzyl chloride.
It is therefore an object of this invention to provide an economical process for producing diphenylalkane which is characterized by good yields, relatively inexpensive reagents, and simplicity.